Humidity sensors have been utilized for controlling the humidity of air-conditioning and heating elements, and detecting the vapor of desiccators and automatic cooking appliances such as ovens and microwaves.
For methods of detecting humidity, a variety of physical and chemical phenomena has been employed. For detecting humidity using an electrical signal, however, methods of sensing the changes in the electric capacitance or the resistance of ceramics and organic macromolecules are generally known. A ceramic humidity sensor employing porous ceramics for a humidity sensing element and a polymer humidity sensor are also well known.
However, the above-noted humidity sensors can be used only in limited environments; in the case of using the sensors in a moist environment, drops of water may stick to a humidity sensing element or the material of the element, polyelectrolyte, thus causing it to melt and thereby degrading characteristics of such sensors.